1. Field of the Invention
The present invention relates to a timer which is resistive or substantially impervious to a power outage which is encountered in the main power supply.
As a rule, a timer of that type is usually equipped with a so-called running reserve for bridging over of transient outages of the main power supply, such that the timer will also continue to operate in a correct time cycle even during the outage or failure of the main power supply, and as a consequence, the normal operation under main power can again proceed upon renewed availability of the main power supply with requiring the setting of the timer to the actual real point in time. The running reserve generally comprises a primary or a secondary battery and a voltage-controlled switching device, The voltage-controlled switching device connects the timer to the main power supply during normal operation, and connects the timer to the secondary battery when the main power-supply voltage falls below a minimum value which is necessary for operation; in essence, especially when the power fails completely due to reasons of operating disruptions caused by the power supply.
2. Discussion of the Prior Art
A timer of this type which is battery-backed for the provision of a running reserve, but which is ordinarily operated from a main power supply, is generally known in the timing control art. Through the operational buffering or support from the built-in running reserve there is ensured that upon the occurrence of a power outage, the time-maintaining advancing sequence of the switching mechanism will continue to run and thereby, at a renewed presence in the main power supply, the power control over the timer will again take place at the specified points in time. However, in having a timer equipped with such a running reserve, it is necessary to provide two driving mechanisms in order to facilitate the time-dependent operation of the timer selectively from either a main power supply or from a battery, which as a rule has a contrastingly lower voltage, or with quite considerably complex converting circuits for the seamlessly smooth operating transition of the driving device between different power sources which are known in the art. Moreover, it is particularly problematic in the utilization of such a power-backed running reserve, that the power storage element or battery, because of aging phenomena, will no longer possess the necessary capacity for the bridging operation. This typically occurs after a multi-year undisrupted operation utilizing the main power, while the running reserve slowly discharges, and there is a failure of the main power supply. The available power storages which come into consideration for the running reserve, especially such as rechargeable batteries are in effect subject to the quite serious disadvantage, that after a few years, as a result of age, there will be encountered an internal short-circuit condition; in effect, they would no longer be available as a bridging source. The short-circuit can even lead to the operating failure for the timer notwithstanding the available or renewedly available main power supply. In particular, at high temperatures of the surroundings, such as can also be encountered in switch boxes, the life expectancy of such power storages sinks rapidly to short residual time periods; while on the other hand, low temperatures of the surroundings lead to a considerably reduced capacity for the electrochemical power storage.